Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$27.37	7.259%	$29.3568	$29.36	$29.35	$29.40
Purchase #2	$66.32	6.753%	$70.7986	$70.80	$70.80	$70.80
Purchase #3	$85.75	10.395%	$94.6637	$94.66	$94.65	$94.70
Purchase #4	$216.33	13.350%	$245.2101	$245.21	$245.20	$245.20
Purchase #5	$138.33	10.831%	$153.3125	$153.31	$153.30	$153.30
Purchase #6	$233.64	8.814%	$254.233	$254.23	$254.25	$254.20
Purchase #7	$144.33	9.404%	$157.9028	$157.90	$157.90	$157.90
7 purchase totals =	$912.07		$1,005.4775	$1,005.47	$1,005.45	$1,005.50